Hey,
at first a picture of the aquarium:
I just try to answer number by number:
1. The aquarium was outdoors. No cover or anything else. There was direct sunlight in the early morning for about one hour. During the rest of the day there was shade because of a hedgerow.
2. As you can see there has only been a piece of cork, but they never used it.
3. As i wrote at 2. they never left the water. So they were under the ice layer.
4. The females didn't use plants or leaves as substrate. They deposited most eggs in clutches around very thin sticks and rarely on branches or cork.
5. There was no filtration or water change from mid of January (when i set up the enclosure) till egg deposition. But there was rain (up to 10 liters altogether I think).
I thought this would be the most natural set-up.
6. they were hibernating in a small box (30x25x25cm) with 20cm forest soil in it. Nothing else, very simple.
Greetings
Mario